Field of the Invention
The present invention relates to an imprint apparatus and a method of manufacturing an article using the same.
Description of the Related Art
The imprint technique uses an optical exposure apparatus to form a fine pattern on a substrate such as a silicon wafer or a glass plate using, as an original, a mold having a fine pattern formed on it. A fine pattern is formed by dispensing/spreading or coating a resin (an imprint material) onto a substrate, and curing the resin while keeping the pattern of a mold in contact with the resin.
The imprint technique includes the heat cycle method and photo-curing method. In the heat cycle method, a thermoplastic resin is heated to the temperature equal to or higher than its glass transition temperature, and a mold is brought into contact with the resin while its fluidity is kept high. After the resin is cured by cooling, the mold is separated from the cured resin. In the photo-curing method, while a mold made of an optically transparent material such as quartz is kept in contact with a resin, the resin is irradiated with ultraviolet rays to cure the resin, and the mold is separated from the cured resin. The heat cycle method prolongs the transfer time due to factors associated with temperature control, and degrades the size accuracy or position accuracy due to changes in temperature. On the other hand, the photo-curing method has no such drawbacks and is therefore advantageously applied to mass production of semiconductor devices.
Until today, a variety of imprint apparatuses have been put into practical use in accordance with the resin curing methods and the purposes of use. Assuming an apparatus is intended for the mass production of, for example, semiconductor devices, an apparatus which exploits a scheme called jet-and-flash imprint lithography (to be abbreviated as J-FIL hereinafter) is effective. An imprint apparatus suitable for J-FIL is disclosed in M. Colburn et al.: “Step and flash imprint lithography: a new approach to high resolution patterning”, Proc. SPIE 3676 “Emerging Lithographic Technologies III” (1999) 379 (non-patent literature 1). Such an imprint apparatus includes a substrate stage, resin dispenser, imprint head, light irradiation system, and positioning alignment mark detection mechanism. An imprint operation is performed by the step-and-repeat scheme, as in a light exposure apparatus.
An alignment operation in the conventional imprint apparatus is performed in the following way. Alignment marks are formed on a substrate and a mold. At the start of an imprint operation for each shot region on the substrate, first, the mold is brought into contact with the resin. The alignment marks formed on the mold are observed through a microscope system with those formed in the shot region to be processed. The mold and the substrate are aligned based on the detected amount of shift, and the resin is cured. After the curing operation, the mold is separated from the substrate, and the process shifts to the next shot region.
The above-mentioned processes are performed for all shot regions. The scheme in which alignment is performed for each shot region is commonly called the die-by-diedie-by-die (D×D) alignment scheme, and widely used in imprint apparatuses. The moire scheme is available as an actual alignment method. The moire scheme has been known since an X-ray exposure apparatus was developed, and is described in, for example, U.S. Pat. No. 7,630,067 (patent literature 1) and E. E. Moon et al.: “Application of interferometric broadband imaging alignment on an experimental x-ray stepper”, J. Vac. Sci. Technol. B 16(6), November/December (1998) 3631 (non-patent literature 2).
Note that in this specification, an operation of bringing the pattern of a mold into contact with a resin, and curing the resin, thereby transferring this pattern onto the resin will be referred to as imprinting or an imprint operation hereinafter. Also, a region which is defined on a substrate and in which a pattern is formed by one imprint operation will be referred to as a shot region hereinafter. One shot region includes one or a plurality of chips. The chip is eventually packaged to fabricate a device.
The alignment scheme adopted in the conventional optical exposure apparatus is called global alignment, in which alignment is performed faithfully to a grid formed on a substrate in advance. In the global alignment scheme, the positions of a reticle and substrate are monitored by a laser interferometer or an encoder with respect to an apparatus reference, thereby aligning them. In this case, it is difficult to directly monitor the positions of a thin reticle and a substrate in practice. Accordingly, the positions of a reticle chuck and a substrate chuck which hold the reticle and the substrate, respectively, are monitored. This requires the system to tightly fix the reticle and the substrate to the reticle chuck and the substrate chuck, respectively, so as to prevent their positions from shifting.
However, in the case of imprinting, not only to bring a mold into contact with a resin on a substrate, but also to separate the mold from the cured resin, give a considerable force between the substrate and the mold. With regard to the substrate, although the substrate is chucked by a substrate chuck by, for example, vacuum suction, it may be pulled in the separation procedure of the mold from the resin, leading to a change in the relative position between the substrate chuck and the substrate on the level of nanometers. When the relative position between the substrate chuck and the substrate changes in the separation procedure, the global alignment scheme cannot be adopted, because it assumes no change in the relative position. Therefore, the die-by-die scheme is advantageous in imprinting, for the mold and the substrate are aligned in each shot so that the movement of the substrate on the substrate chuck can be compensated.
Instead of the global alignment used in optical exposure apparatus, the die-by-die scheme is adopted in imprinting for the above-mentioned special reason. However, the die-by-die scheme has rarely been used in the conventional alignment operation for full-scale semiconductor mass production. The following problem is posed.
In the global alignment scheme, since a grid formed on a substrate in advance is used, shot regions in which a new grid is formed after the global alignment have a strong correlation between them with the grids' matching. However, in the die-by-die scheme, since alignment and imprint operations are repeated for each shot, the shot regions have no correlation between the former grid after alignment because there exists no grid formation concept in the die-by-die system.
In the conventional global alignment scheme, the alignment state of the entire shots on the substrate can be analogically determined based on the above-mentioned correlation. The alignment status of the substrate can be inspected through observing only several shots within the substrate. On the other hand, in the die-by-die scheme, the shot regions have no correlation each other, so the alignment status of the entire substrate cannot be determined by sampling a small number of shots within the substrate. More specifically, it is necessary to inspect all shot regions. Inspection of all shot regions is impractical in terms of time and cost.